Cataract extraction is one of the most commonly performed surgical procedures in the world with estimates of 2.5 million cases being performed annually in the United States and 9.1 million cases worldwide. This is expected to increase to approximately 13.3 million cases by 2006 globally. This market is composed of various segments including intraocular lenses for implantation, viscoelastic polymers to facilitate surgical maneuvers, disposable instrumentation including ultrasonic phacoemulsification tips, tubing, and various knives and forceps. Modern cataract surgery is typically performed using a technique termed phacoemulsification in which an ultrasonic tip with an associated water stream for cooling purposes is used to sculpt the relatively hard nucleus of the lens after performance of an opening in the anterior lens capsule termed anterior capsulotomy or more recently capsulorhexis. Following these steps as well as removal of residual softer lens cortex by aspiration methods without fragmentation, a synthetic foldable intraocular lens (IOL's) inserted into the eye through a small incision. This technique is associated with a very high rate of anatomic and visual success exceeding 95% in most cases and with rapid visual rehabilitation.
One of the earliest and most critical steps in the procedure is the performance of capsulorhexis. This step evolved from an earlier technique termed can-opener capsulotomy in which a sharp needle was used to perforate the anterior lens capsule in a circular fashion followed by the removal of a circular fragment of lens capsule typically in the range of 5-8 mm in diameter. This facilitated the next step of nuclear sculpting by phacoemulsification. Due to a variety of complications associated with the initial can-opener technique, attempts were made by leading experts in the field to develop a better technique for removal of the anterior lens capsule preceding the emulsification step. These were pioneered by Neuhann, and Gimbel and highlighted in a publication in 1991 (Gimbel, Neuhann, Development Advantages and Methods of the Continuous Curvilinear Capsulorhexis. Journal of Cataract and Refractive Surgery 1991; 17:110-111, incorporated herein by reference). The concept of the capsulorhexis is to provide a smooth continuous circular opening through which not only the phacoemulsification of the nucleus can be performed safely and easily, but also for easy insertion of the intraocular lens. It provides both a clear central access for insertion, a permanent aperture for transmission of the image to the retina by the patient, and also a support of the IOL inside the remaining capsule that would limit the potential for dislocation.
Using the older technique of can-opener capsulotomy, or even with the continuous capsulorhexis, problems may develop related to inability of the surgeon to adequately visualize the capsule due to lack of red reflex, to grasp it with sufficient security, to tear a smooth circular opening of the appropriate size without radial rips and extensions or technical difficulties related to maintenance of the anterior chamber depth after initial opening, small size of the pupil, or the absence of a red reflex due to the lens opacity. Some of the problems with visualization have been minimized through the use of dyes such as methylene blue or indocyanine green. Additional complications arise in patients with weak zonules (typically older patients) and very young children that have very soft and elastic capsules, which are very difficult to mechanically rupture.
Finally, during the intraoperative surgical procedure, and subsequent to the step of anterior continuous curvilinear capsulorhexis, which typically ranges from 5-7 mm in diameter, and prior to IOL insertion the steps of hydrodissection, hydrodilineation and phaco emulsification occur. These are intended to identify and soften the nucleus for the purposes of removal from the eye. These are the longest and thought to be the most dangerous step in the procedure due to the use of pulses of ultrasound that may lead to inadvertent ruptures of the posterior lens capsule, posterior dislocation of lens fragments, and potential damage anteriorly to the corneal endothelium and/or iris and other delicate intraocular structures. The central nucleus of the lens, which undergoes the most opacification and thereby the most visual impairment, is structurally the hardest and requires special techniques. A variety of surgical maneuvers employing ultrasonic fragmentation and also requiring considerable technical dexterity on the part of the surgeon have evolved, including sculpting of the lens, the so-called “divide and conquer technique” and a whole host of similarly creatively named techniques, such as phaco chop, etc. These are all subject to the usual complications associated with delicate intraocular maneuvers (Gimbel. Chapter 15: Principles of Nuclear PhacoEmulsification. In Cataract Surgery Techniques Complications and Management. 2.sup.nd ed. Edited by Steinert et al. 2004: 153-181, incorporated herein by reference
Following cataract surgery one of the principal sources of visual morbidity is the slow development of opacities in the posterior lens capsule, which is generally left intact during cataract surgery as a method of support for the lens, to provide good centration of the IOL, and also as a means of preventing subluxation posteriorly into the vitreous cavity. It has been estimated that the complication of posterior lens capsule opacification occurs in approximately 28-50% of patients (Steinert and Richter. Chapter 44. In Cataract Surgery Techniques Complications and Management. 2.sup.nd ed. Edited by Steinert et al. 2004: pg. 531-544 and incorporated herein by reference). As a result of this problem, which is thought to occur as a result of epithelial and fibrous metaplasia along the posterior lens capsule centrally from small islands of residual epithelial cells left in place near the equator of the lens, techniques have been developed initially using surgical dissection, and more recently the neodymium YAG laser to make openings centrally in a non-invasive fashion. However, most of these techniques can still be considered relatively primitive requiring a high degree of manual dexterity on the part of the surgeon and the creation of a series of high energy pulses in the range of 1 to 10 mJ manually marked out on the posterior lens capsule, taking great pains to avoid damage to the intraocular lens. The course nature of the resulting opening is illustrated clearly in FIG. 44-10, pg. 537 of Steinert and Richter, Chapter 44 of In Cataract Surgery Techniques Complications and Management. 2.sup.nd ed (see complete cite above).
What is needed are ophthalmic methods, techniques and apparatus to advance the standard of care of cataract and other ophthalmic pathologies.